(6ix) Biomolecular Engineering and Magnetic Resonance for Structural Biology and Synthetic Biology

Methods based on the physical principle of magnetic resonance, such as magnetic resonance imaging (MRI), utilize electromagnetic waves and magnetic field to noninvasively probe the location and structure of molecules. While MRI provides spatial information of molecules, its twin brother, nuclear magnetic resonance (NMR) spectroscopy, aims to probe the atomic-resolution details within a given molecule. Similarly, NMR is a unique noninvasive structural biology method that can study proteins under physiological hydration and temperature and in some cases, inside living cells. My scientific goals are to use biomolecular engineering to innovate NMR and MRI methods, allowing previously unattainable studies of molecules in intact cells and tissues, and on the other hand, to use NMR and MRI to characterize the performance of engineered molecules and cells.

As an example of this approach, I engineered biomolecular contrast agents that enabled acoustically modulated magnetic resonance imaging (AM-MRI), a new variant of MRI that uses ultrasound modulation [1-3]. While MRI can provide whole-body images at high resolution, there is a paucity of genetically encoded contrast agents, equivalent to green fluorescent protein (GFP) for optical imaging, that can enable MRI to visualize specific cellular processes such as gene expression. To address this technological gap, I engineered gas vesicles (GVs), a class of hollow gas-filled protein nanostructures evolved in photosynthetic microbes. The air inside GVs enabled their detection by MRI, and uniquely, such contrast was erasable by ultrasound treatment, which permitted selective imaging of these agents in the presence of background tissue contrast and solved a major issue that had plagued the use of existing MRI contrast agents.

While genetically encoded MRI contrast agents enabled the imaging of gene expression in vivo, my PhD research focused on the development of novel solid-state NMR (ssNMR) methods for studying atomic-resolution structure and function of membrane proteins in their native lipid bilayer environment. My research ranged from quantum mechanics theory of NMR pulse sequences [4-5], novel resonance assignment methods [6-8], to structure determination of a mercury transporter protein [9], which both demonstrated the frontier of the methodology and provided important insights into the bacterial mercury bioremediation pathway.

By working at the interface of two different disciplines – biomolecular engineering and magnetic resonance – we can develop innovative technologies and insights that will influence both basic biology research and the development of macromolecular and cellular therapeutics.

Selected Publications:

1. Lu GJ, Farhadi A, Szablowski JO, Lee-Gosselin A, Barnes SR, Lakshmanan A, Bourdeau RW, Shapiro MG (2018) Acoustically modulated magnetic resonance imaging of gas-filled protein nanostructures. Nature Materials 17:456–463. News and views. Journal front cover.
2. Lu GJ #, Farhadi A #, Mukherjee A, Shapiro MG (2018) Proteins, air and water: reporter genes for ultrasound and magnetic resonance imaging. Curr. Opin. Chem. Biol. 45:57-63. (# co-author)
3. Lakshmanan A #, Lu GJ #, Farhadi A #, Nety SP #, Kunth M, Lee-Gosselin A, Maresca D, Bourdeau RW, Yin M, Yan J, Witte C, Malounda D, Foster FS, Schröder L, Shapiro MG. (2017) Preparation of biogenic gas vesicle nanostructures for use as contrast agents for ultrasound and MRI. Nature Protocols 12(10):2050-2080. (# co-author)
4. Lu GJ, Opella SJ (2014) Mechanism of dilute-spin-exchange in solid-state NMR. J. Chem. Phys. 140(12):124201.
5. Lu GJ, Opella SJ (2013) Motion-adapted pulse sequences for oriented sample (OS) solid-state NMR of biopolymers. J. Chem. Phys. 139(8):084203.
6. Lu GJ, Park SH, Opella SJ (2012) Improved ¹H amide resonance line narrowing in oriented sample solid-state NMR of membrane proteins in phospholipid bilayers. J. Magn. Reson. 220:54-61.
7. Lu GJ, Son WS, Opella SJ (2011) A general assignment method for oriented sample (OS) solid-state NMR of proteins based on the correlation of resonances through heteronuclear dipolar couplings in samples aligned parallel and perpendicular to the magnetic field. J. Magn. Reson. 209(2):195-206.
8. Lu GJ, Opella SJ (2014) Resonance assignments of a membrane protein in phospholipid bilayers by combining multiple strategies of oriented sample solid-state NMR. J. Biomol. NMR 58(1): 69-81.
9. Lu GJ, Tian Y, Vora N, Marassi FM, Opella SJ (2013) The structure of the mercury transporter MerF in phospholipid bilayers: a large conformational rearrangement results from N-terminal truncation. J. Am. Chem. Soc. 135(25):9299-9302.
10. Lu GJ, Garen CR, Cherney MM, Cherney LT, Lee C, James MNG (2007) Expression, purification and preliminary X-ray analysis of the C-terminal domain of an arginine repressor protein from Mycobacterium tuberculosis. Acta Crystallogr F 63(Pt 11):936-939.

Awards/Honors:

Lu GJ (P.I.), Shapiro MG, Tirrell DA (mentors) NIH Pathway to Independence Award (K99/R00) Starting 08/2018.

Teaching Interests:

I like to implement an active learning environment in the classroom and have hands-on experience in teaching both laboratory course and lecture. In graduate school, I served as a teaching assistant in analytical chemistry laboratory, and presented weekly tutorial seminars for protein biochemistry course. At Caltech, I have given lectures in the Molecular Imaging course offered in the Chemical Engineering department. My Ph.D. background in chemistry and biochemistry offer a unique angle for me to teach in a Chemical Engineering department, while my exposure to quantitative physics and multidisciplinary research gives me confidence and enthusiasm to teach in various disciplines.